Pain to cold food ingestion following root canal therapy: where is the source?

Two cases of pain evoked by cold food ingestion, following root canal therapy, are presented. The source of pain was detected when cold application to the vestibular, periapical area corresponding to the teeth involved evoked strong pain of about 30-second durations. In the first case, the patient suffered from strong pain in the mandibular right area over the last 4 months. After successive root canal therapy of three mandibular right teeth, the spontaneous pain eased significantly, but strong pain evoked by cold food ingestion persisted. Cold application to the vestibular periapical area of teeth involved identified the source of pain, which was abolished by 80 mg/day of slow-release propranolol. In the second case, cold allodynia developed after root canal therapy. The root canal therapy was performed for prosthetic reasons with no prior pain. Pain could be duplicated by cold application to the vestibular area of the treated tooth. The patient preferred no treatment when the source of pain was explained. In both cases cold application did not produce any pain in other intraoral locations, including the contralateral vestibular area or the mid soft or hard palate. Pain mechanisms, neurovascular and neuropathic, which differ for each case are discussed.